In Vitro and In Vivo Effects of Palmaria palmata Derived Peptides on Glucose Metabolism

International Journal of Peptide Research and Therapeutics (2021) 27:1667–1676 https://doi.org/10.1007/s10989-021-10199-8 In Vitro and In Vivo Effects of Palmaria palmata Derived Peptides on Glucose Metabolism Pádraigín A. Harnedy‑Rothwell1,2 · Chris M. McLaughlin3 · Aurélien V. Le Gouic1 · Ciaran Mullen3 · Vadivel Parthsarathy3 · Philip J. Allsopp3 · Emeir M. McSorley3 · Richard J. FitzGerald1,2 · Finbarr P. M. O’Harte3 Accepted: 16 March 2021 / Published online: 29 March 2021 © The Author(s) 2021 Abstract Three synthetic peptides, ILAP, LLAP and MAGVDHI, derived from a Palmaria palmata protein hydrolysate were assessed for their antidiabetic potential in vitro and in vivo. In addition to inhibiting dipeptidyl peptidase-IV in a cell-based in situ assay all three peptides significantly increased the half-life of the incretin hormone glucagon-like peptide-1 (GLP-1). ILAP and LLAP mediated a significant increase (p < 0.001) in insulin secretion from BRIN-BD11 cells compared to the glucose control, while MAGVDHI had no insulinotropic activity at an eqimolar concentration ( 10–6 M). A significant increase in the concentration of cyclic adenosine monophosphate production in BRIN-BD11 cells mediated by ILAP (p < 0.001) and LLAP (p < 0.01) compared to the basal control, would indicate that insulin secretion may be mediated by membrane based activation. Furthermore, ILAP and LLAP acted as glucose-dependent insulinotropic polypeptide (GIP) secretagogues, stimulating a significant increase (p < 0.01) in the concentration of GIP released from enteroendocrine STC-1 cells compared to the glucose control. When tested in vivo in healthy male NIH Swiss mice, ILAP and LLAP, mediated a significant increase (p < 0.01) in plasma insulin and decrease (p < 0.05) in blood glucose, respectively, compared to the control. MAGVDHI mediated a significant (p < 0.001) sustained reduction in food intake in food deprived trained mice. These results demonstrate that the Palmaria palmata peptides studied herein have prospective antidiabetic activity and have the potential to act as agents that can be used alone or in combination with drugs, to aid in the prevention and management of Type 2 diabetes mellitus. Keywords Bioactive peptides · Dipeptidyl peptidase-IV (DPP-IV) inhibition · Glucagon-like peptide-1 (GLP-1) · Glucosedependent insulinotropic polypeptide (GIP) · Type 2 diabetes · Palmaria palmata Abbreviations ACN Acetonitrile AMC H-Gly-Pro-7-amino-4-methyl coumarin AUC Area under the curve BW Body weight cAMP Cyclic adenosine monophosphate DMEM Dulbecco’s modified Eagle’s medium DPP-IV Dipeptidyl peptidase-IV * Finbarr P. M. O’Harte 1 Department of Biological Sciences, University of Limerick, Limerick, Ireland 2 Health Research Institute (HRI), University of Limerick, Limerick, Ireland 3 School of Biomedical Sciences, Ulster University, Coleraine, Co. Derry, Northern Ireland EDTA Ethylenediaminetetraacetic acid ELISA Enzyme-linked immunosorbent assay FBS Fetal bovine serum GIP Glucose-dependent insulinotropic polypeptide GLP-1 Glucagon-like peptide-1 HBSS Hank’s buffered saline solution ILAP Isoleucine–leucine–alanine–proline IP Intraperitoneal IPI Isoleucine–proline–isoleucine KRBB Krebs–Ringer bicarbonate buffer LDH Lactate dehydrogenase LLAP Leucine–leucine–alanine–proline MALDI-TOF MS Matrix assisted laser desorption ionisation time of flight mass spectrometry MAGVDHI Methionine–alanine–glycine–valine– aspartic acid–histidine–isoleucine 13 Vol.:(0123456789) 1668 International Journal of Peptide Research and Therapeutics (2021) 27:1667–1676 m/z Mass to charge ratio PBS Phosphate buffered saline RP-HPLC Reversed phase-high performance liquid chromatography TFA Trifluoroacetic acid T2DM Type 2 diabetes mellitus Introduction Type 2 diabetes mellitus (T2DM) is a chronic metabolic condition characterised by a deficiency in the secretion and/ or function of insulin (i.e., insulin resistance), resulting in high blood glucose levels (hyperglycaemia; NMIC 2017). With the prevalence of T2DM increasing worldwide, in particular in countries with increasing obesity incidences, effective interventions are required to prevent and manage the condition. Initial approaches to the management of T2DM includes lifestyle modification, particularly in relation to diet and exercise (NMIC 2017). However, these modifications are often insufficient to achieve satisfactory glycaemic control and pharmacological interventions are required. In recent years, a particular focus has been placed on the development of gut hormone-based therapies, which stimulate the biological activities and/or prolong the action of endogenous incretin hormones (Irwin and Flatt 2015). These include glucagon-like peptide-1 receptor (GLP-1R) agonists (incretin mimetics) and dipeptidyl peptidase (DPP)IV inhibitors. Intestinal derived incretin peptides, GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), play a significant role in postprandial insulin release (Green et al. 2004). However, GLP-1 and GIP are rapidly degraded by the aminopeptidase DPP-IV resulting in the loss of their insulinotropic potential in vivo (Deacon 2019). As peptidomimetics, GLP-1R agonists mimic the actions of the endogenous hormone GLP-1, where the structural modifications increase their stability and bioavailability for activation of the receptor, while DPP-IV inhibitors increase the half-life of circulating incretin hormones (Power et al. 2014; Irwin and Flatt 2015; Deacon 2019). Although most synthetic GLP-1 mimetics and DPP-IV inhibitory agents are well tolerated, adverse side-effects, such as mild infections (common cold, urinary and upper respiratory tract infections), headaches, mild to moderate nausea, vomiting and diarrhoea have been reported (Krushner and Gorrell 2010; Lund et al. 2014). While safety concerns linking GLP-1 therapy with pancreatitis, pancreatic and thyroid cancer and glucagon-producing neuroendocrine tumours have been alleviated, pharmacovigilance around the use of GLP-1 drugs is still required, particularly in relation to patients with increased risk or a history of pancreatitis or thyroid cancer (Irwin and Flatt 2015). Furthermore, to date, the development of incretin mimetics has been directed 13 predominantly towards single molecules that modulate individual peptide receptor targets. However, future research aims to identify multi‐agonist components which simultaneously modulate multiple receptor signalling pathways. This may be the identification of single components with multifunctional activities or the generation of designer hybrid peptides that can modulate multiple regulatory peptide hormone receptor pathways (Irwin and Flatt 2015; Brandt et al. 2018). Due to the adverse side-effects posed by existing synthetic T2DM drugs the identification of natural agents that can be used alone or in combination with T2DM drugs, to aid in the prevention and management of T2DM has gained significant (...truncated)